This invention relates to an improved apparatus and technique for determining combustible and oxygen concentration in a combustible fuel environment. By monitoring both the concentration of the oxygen and the concentration of the combustible it is possible to maintain an environment in which the most efficient burning of the combustible is achieved.
To appreciate the usefulness of the invention one must understand the details of the combustion process. By way of example, it is useful to examine the combustion (or oxidation) of carbon monoxide in an oxygen environment. Tow molecules of carbon monoxide react with one molecule of oxygen to yield two molecules of carbon dioxide plus a given amount of heat. The most efficient burning of the carbon monoxide occurs when the ideal stoichiometric ratio of two moles of carbon dioxide is burned in one mole of oxygen. If either the carbon monoxide concentration exceeds or is less than this ideal relationship, the burning is inefficient.
Consider an example where the carbon monoxide concentration exceeds the ideal situation. In this instance the excess carbon monoxide tends to inhibit the combustion process. If the carbon monoxide concentration is too high, the burning may become extinguished and the reaction may need to be restarted. If, during this restart process, oxygen concentration is accidentally increased, there may result a spontaneous energy release which may be destructive.
In the opposite situation where the carbon monoxide concentration decreases from the optimum level, there is an excess of oxygen for the amount of carbon monoxide present in the system. Under those circumstances, energy efficiency is lost in heating the excess oxygen (or air) in the system. Thus for safety and for cost efficiency reasons, it would be preferable to maintain carbon monoxide and oxygen concentrations at the optimum level.
From the above examples it would seem readily apparent that the optimum situation is achieved in which both the oxygen and the carbon monoxide concentration of the fuel can be monitored during the combustion process to assure that the levels of each remain in approximately the correct stoichiometric concentrations.
To the knowledge of the present inventor, the prior art discloses no unitary apparatus for scientifically determining the relative concentrations of both the oxygen and the combustible constituents of a fuel mixture continuously in a harsh industrial environment containing sulfur dioxide. U.S. Pat. No. 3,960,500 to Ross et al discloses a technique and apparatus for determining the oxygen concentration of a gas sample. However, it is apparent that not only the oxygen concentration but also the combustible concentration is necessary to determine whether the necessary stoichiometric relationship exists between the two.
It is the purpose of the present invention to meet this prior art deficiency in a mamnner which enables the determination experimentally of the relative concentrations of not only the oxygen but also the combustible continuously in the burning environment. The present invention achieves this capability by sampling the gaseous environment and routing this sample through a conduit means which divides the sample into three portions. A common aspirator or eductor is utilized to cause a pressure drop in this conduit, which causes the sample to flow into the three portions and thereby causes it to flow past two sensors.
One of the sensors is an oxygen analyzer and the other is a combustibles analyzer. The oxygen analyzer uses a voltaic reaction in a zirconium oxide crystal structure doped with certain predetermined impurities to determine the percentage concentration of oxygen molecules in the gas sample. The combustibles analyzer utilizes a thermopile technique for determining the concentration of combustible element within the sample. Since the combustibles analyzer of the present invention operates at an elevated temperature, the conduit portion routing this sample includes a labyrinth heater with surfaces that radiate heat to the sample before its concentration is analyzed. In the example noted previously, it is possible for this combustible element analyzer to determine the concentration of carbon monoxide in the sample routed through it. By monitoring the concentrations obtained from these two devices, it is possible for the system user to adjust the combustible and oxygen environment until the sensors indicate that the concentrations are at or near the optimum levels. This real time monitoring of combustible and oxygen concentration results, therefore, in considerable cost savings, safety, and increased efficiency in the combustion system.
The above and other features and advantages of the invention will become more apparent as the invention becomes better understood from the detailed description that follows, when considered in connection with the accompanying drawings.